Iso- And Homeostructuralism of Analogous Ph4E and Ph3E-E'R3 Compounds (E = C, Si, Ge, Sn, Pb; E' = Si, Ge, Sn; R = Me, Ph): Crystal Structure of 1,1,1-Trimethyltriphenyldistannane

Full text of DOI:10.1021/ic960791z

6622
Inorg. Chem. 1996, 35, 6622-6624
Notes
Table 1. Crystal Data and Structure Refinement Details for V
Iso- and Homeostructuralism of Analogous Ph4E
and Ph3E-E′R3 Compounds (E ) C, Si, Ge, Sn,
Pb; E′ ) Si, Ge, Sn; R ) Me, Ph): Crystal
Structure of 1,1,1-Trimethyltriphenyldistannane
empirical formula ) C21H24Sn2
fw ) 513.78
space group P3h (No. 147)
T ) 20(2) °C
a ) 11.739(3) Å
c ) 8.871(4) Å
V ) 1058.7(6) Å3
Z ) 2
λ ) 0.710 73 Å
F
calcd ) 1.612 g cm-3
R1a ) 0.0301
wR2b ) 0.0651
La´szlo´ Pa´rka´nyi,*,† Alajos Ka´lma´n,†
Keith H. Pannell,*,‡ Francisco Cervantes-Lee,‡ and
Ramesh N. Kapoor‡
µ ) 23.57 cm-1
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑w(Fo2 - Fc2)/∑w(Fo )2]1/2
.
2
Central Research Institute for Chemistry,
Hungarian Academy of Sciences, P.O. Box 17,
H-1525 Budapest, Hungary, and Department of Chemistry,
The University of Texas at El Paso,
Ph3Ge-GeMe3)8 crystallize in space group P3h (No. 147). The
high index1 of isostructurality (Ii(23) ) 95%) between Ph3Si-
SiMe3 and Ph3Ge-SiMe3 is also observed between its isomers
Ph3Si-GeMe3 and Ph3Ge-GeMe3 (94%). When one of the
core atoms of Ph3Ge-GeMe3 is replaced by the larger Sn atom,
the new isomers IVa, Ph3Ge-SnMe3, and IVb, Ph3Sn-GeMe3
(group b, space group Pna21 (No. 33)),9 are no longer iso-
structural with group a. Kitaigorodskii expected such “mor-
photropic” phase transitions whenever the atomic replacement
diminishes the existing packing coefficient.2 The Ge-Sn
isomers remain isostructural and can substitute one another in
the crystal lattice, forming solid solutions.10 In the new
pseudohexagonal unit cells (Pna21), the bumps of the Ph3Ge-
SnMe3 and Ph3Sn-GeMe3 molecules stacked with similar
orientations along the polar c axis fit perfectly into the hollows
of the adjacent columns generated by the glide planes.11 No
structural data have been reported for the series Ph3E-E′Me3
(E ) E′ ) C, Sn, Pb); therefore the reason for this grouping is
not apparent. It may depend on the size (radius) of the core
atoms and/or on their radius difference. The present work on
the structure determination of Ph3Sn-SnMe3 (V) aims to fill
in, at least in part, this gap.
El Paso, Texas 79968-0513
ReceiVed July 3, 1996
Introduction
The strict rules1 limiting the formation of similar packing
arrays restrict organic crystals from exhibiting isostructurality,
which along with crystal polymorphism is governed by the effort
to gain the maximum of close packing. Molecular associations
strive for attainment of the maximum density by bringing the
bumps of the molecules of irregular shape into the hollows of
the adjacent molecules Via the optimum symmetry operations
permitted within the seven crystal systems.2 In principle, only
isometric molecules can form isostructural crystals; otherwise,
only relaxed relationships, termed as homeostructural, can be
expected.
The quadrivalent C, Si, Ge, Sn, and Pb atoms screened by
their alkyl and/or aryl substituents can be replaced by each other
without altering the outer shape of the molecules, presenting
an attractive series for investigating the conditions of isostruc-
turality. The substantial change of the covalent radii of C to
Pb (re ) 0.77 Vs 1.40 Å) may lead to phase transitions. The
tetraphenyl derivatives (Ph4E) of the group 14 elements crystal-
lize in the tetragonal space group P4h21c, (No. 114).3 The
increasing radii of the core atoms do not terminate their identical
close packing. The analogous Ph3E-E′Ph3 derivatives (E )
E′ ) Ge, Sn, Pb) also exhibit isostructuralism, but their packing
relationship is modulated by additional pseudosymmetries and
disorder.4
Experimental Section
Synthesis.12 A solution of 1.93 g (5 mmol) of Ph3SnCl in 15 mL
of THF was added to Li, 0.35 g (50 mmol), stirred in 15 mL of THF.
After 1 h, the color changed, and after 12 h, a dark green solution was
obtained. This was transferred Via canula to a dropping funnel and
added dropwise to a cooled solution of Me3SnCl, 0.99 g (5 mmol).
Upon slow addition, the color disappeared, and after 30 min of stirring,
the solvent was removed in vacuo. Recrystallization from hexane/
methylene chloride resulted in crystals of Ph3SnSnMe3 suitable for
X-ray analysis.
Isostructurality is also a recurrent phenomenon among the
Ph3E-E′Me3 derivatives (E ) Si, Ge, Sn). Group a complexes
(I, Ph3Si-SiMe3;5 IIa, Ph3Si-GeMe3;6 IIb, Ph3Ge-SiMe3;7 III,
X-ray Structure. A transparent prism crystal (0.60 × 0.40 × 0.20
mm) was mounted on a Siemens R3m/V four-circle diffractometer using
graphite-monochromated Mo KR radiation at room temperature.
Crystallographic data and refinement details are given in Table 1.
Intensities of three standard reflections were measured after each 100
reflections, and these remained constant throughout the data collection.
The structure was solved by the heavy-atom method. Full-matrix
anisotropic least-squares refinement was carried out on F2 using the
† Hungarian Academy of Sciences.
‡ The University of Texas at El Paso.
(1) Ka´lma´n, A.; Pa´rka´nyi, L.; Argay, Gy. Acta Crystallogr., Sect. B 1993,
49, 1039.
(2) Kitaigorodskii, A. I. Organic Chemical Crystallography; Consultants
Bureau: New York, 1961; p 223.
(3) (a) Robbins, A.; Jeffrey, G. A.; Chesick, J. P.; Donohue, J.; Cotton,
F. A.; Frenz, B. A.; Murillo, C. A. Acta Crystallogr., Sect. B 1975,
31, 2395. (b) Gruhnert, V.; Kirfel, A.; Will, G.; Wallrafen, F.; Recker,
K. Z. Kristallogr. 1983, 163, 53. (c) Karipides, A.; Haller, D. A. Acta
Crystallogr., Sect. B 1972, 28, 2889. (d) Belsky, V.; Simonenko, A.
S.; Reikhsfeld, V. O.; Saratov, I. E. J. Organomet. Chem. 1983, 244,
125. (e) Busetti, V.; Mammi, M.; Signor, A.; Del Pra, A. Inorg. Chim.
Acta 1967, 1, 424.
(4) Kleiner, N.; Dra¨ger, M. J. Organomet. Chem. 1984, 270, 151.
(5) Pa´rka´nyi, L.; Hengge, E. J. Organomet. Chem. 1982, 235, 273.
(6) Pannell, K. H.; Raptis, R.; Kapoor, R. N.; Pa´rka´nyi, L.; Fu¨lo¨p, V. J.
Organomet. Chem. 1990, 384, 41.
(7) Pa´rka´nyi, L.; Hernandez, C.; Pannell, K. H. J. Organomet. Chem. 1986,
301, 145.
(8) Pa´rka´nyi, L.; Ka´lma´n, A.; Sharma, S.; Nolen, D. M.; Pannell, K. H.
Inorg. Chem. 1994, 33, 180.
(9) Pannell, K. H.; Pa´rka´nyi, L.; Sharma, H.; Cervantes-Lee, F. Inorg.
Chem. 1992, 31, 522.
(10) Pa´rka´nyi, L.; Ka´lma´n, A.; Pannell, K. H.; Sharma, H. K. J. Organomet.
Chem. 1994, 484, 193.
(11) Ka´lma´n, A.; Pa´rka´nyi, L.; Argay, Gy. Acta Chim. Hung. 1993, 130,
279.
(12) Mitchell, T. N.; Guntram, W. J. Chem. Soc., Perkin Trans. 2 1977,
1842.
S0020-1669(96)00791-4 CCC: $12.00 © 1996 American Chemical Society

Notes
Inorganic Chemistry, Vol. 35, No. 22, 1996 6623
Table 2. Bond Lengths (Å) and Angles (deg)a
Sn1-C1
Sn1-Sn2
Sn2-C7
C1-C2
C1-C6
2.152(4)
2.7820(14)
2.138(5)
1.373(6)
1.384(6)
C2-C3
C3-C4
C4-C5
C5-C6
1.380(7)
1.360(8)
1.382(8)
1.368(7)
C1-Sn1-C1i
C1-Sn1-Sn2
C7-Sn2-C7ii
C7-Sn2-Sn1
C2-C1-C6
105.48(12)
113.21(10)
108.1(2)
110.8(2)
117.4(4)
120.4(3)
C6-C1-Sn1
C3-C2-C1
C4-C3-C2
C3-C4-C5
C6-C5-C4
C5-C6-C1
122.2(3)
121.4(4)
120.2(5)
119.6(5)
119.5(5)
121.9(5)
C2-C1-Sn1
a Symmetry transformations used to generate the complete molecule:
(i) -y + 1, x - y + 1, z; (ii) -x + y, -x + 1, z.
Figure 2. Relative positions of I, III, and V (full line) in the unit cell
of I: (a) view perpendicular to the 3-fold axis; (b) view down the 3-fold
axis.
(2.770(4) Å) was observed in the hexaphenyl derivative.15 An
extremely long Sn-Sn bond of 3.034(1) Å was reported for
tetra-tert-butyl-1,2-bis(2,4,6-triisopropylphenyl)distannane, which
adopts an unusual conformation in the crystal with all bulky
aryl moieties in the syn orientation and eclipsed Sn-C bonds.16
The Sn-Sn bond length in the hexa-tert-butyl compound is
2.894(1) Å.17 The E-E bond length difference between the
corresponding Ph3E-EMe3 and t-Bu6E2 compounds decreases
with the increasing E-E bond length (∆(Si-Si) ) 0.34, ∆(Ge-
Ge) ) 0.28, ∆(Sn-Sn) ) 0.11 Å), showing a significant
reduction of steric crowding.17-19
The lack of isometricity between the molecules of group a
and V is equally responsible for the shifting of V along the
3-fold axis and a rotation of the molecule by 23° with reference
to the disilane (Figure 2b). The best planes of the phenyl rings
also turn by 24.5°, forming a smaller dihedral angle (52.7°) with
the 3-fold axis (I: 57.1°).
Isostructuralism and Morphotropic Phase Transitions.
The systematic replacement of the core atoms in the Ph3E-
E′Me3 series from Si-Si to Sn-Sn gives rise to two morpho-
tropic phase transitions as presented in Figure 3.
Figure 1. Molecular diagram with the numbering of atoms. Thermal
ellipsoids represent 50% probabilities.
The c crystallographic axis slightly elongates upon going from
the disilane to the digermane (∆c(III-I) ) 0.122 Å), and it
shortens from digermane to distannane (∆c(V-III) ) -0.068
Å), yielding a value that is close to the c axis of the disilane
(∆c(V-I) ) 0.054 Å). The greatest change is perceivable in
the lengths of the a axes (∆a(III-I) ) 0.022, ∆a(V-I) ) 0.426,
∆a(V-III) ) 0.404 Å). The unit cell volume differences are
as follows: ∆V(III-I) ) 17.3, ∆V(V-I) ) 81.4 ∆V(V-III)
) 64.1 Å3.
SHELXL program.13 Atomic positions for the hydrogen atoms were
calculated from assumed geometries, and they were treated as riding
atoms. A common U(iso) temperature factor was refined for the phenyl
hydrogens, and another, for the methyl hydrogen atoms. The scattering
factors used were taken from ref 14. Selected bond lengths and angles
are given in Table 2, and the structure is depicted in Figure 1.
Discussion
In contrast, the tetragonal unit cells assumed by the isostruc-
tural Ph4E homologs (with two molecules in the asymmetric
unit) are flattened in a stepwise mode as if pressed along the
principal c axis. The change in the a/c ratio seems to be
proportional to the increase of the atomic radii, showing the
greatest difference between the C and Pb homologues. This
phenomenon underscores our earlier conclusion concerning the
relationship between the unit cells of the isostructural pairs
expressed by eq 1 given in ref 1.
Molecular Geometry and Packing. V crystallizes in space
group P3h (group a), and the unit cell indicates that it might be
isostructural with other members of this group. The atomic
coordinates, however, testify only a relaxed relationship, since
the molecule adopts a different position in the unit cell. Placing
the title compound and III in the unit cell of disilane I, one
can see the difference in the relative positions of the two
molecules as shown in Figure 2. This comparison reveals that
molecule V is no longer isometric with I, IIa, IIb, and III (group
a). While the E-E′ distance for group a varies 1% about the
mean 2.388(26) Å, the Sn-Sn bond distance [2.782(1) Å] is
longer by 16.5%. Consequently, the packing relationship of V
with I-III is a par excellence case of homeostructuralism.1
In the crystal structures of Ph4E and Ph3E-E′Me3 derivatives
(except IVa and IVb with Sn-Ge cores), the molecular
(15) Preut, H.; Haupt, H.-J.; Huber, F. Z. Anorg. Allg. Chem. 1973, 396,
81.
(16) Weidenbruch, M.; Schlaefke, J.; Peters, K.; von Schnering, H. G. J.
Organomet. Chem. 1991, 414, 319.
(17) Puff, H.; Breuer, B.; Gehrke-Brinkmann, G.; Kind, P.; Reuter, H.;
Schuh, W.; Wald, W.; Weidenbruck, G. J. Organomet. Chem. 1989,
363, 265.
The Sn-Sn bond length falls in the range of bonds reported
for linear Sn-Sn bonds (2.77-2.89 Å). The shortest bond
(13) Sheldrick, G. M. SHELXL93: Program for the Refinement of Crystal
Structures. University of Go¨ttingen, Germany, 1994.
(14) International Tables for Crystallography; Kluwer Academic Publish-
ers: Dordrecht, The Netherlands, 1992; Vol. C.
(18) Wiberg, N.; Schuster, H.; Simon, A.; Peters, K.; von Schnering, H.
G. Angew. Chem., Int. Ed. Engl. 1986, 25, 79.
(19) Weidenbruch, M.; Grimm, F. T.; Herrndorf, M.; Scha¨fer, A.; Peters,
K.; von Schnering, H. G. J. Organomet. Chem. 1988, 341, 335.

6624 Inorganic Chemistry, Vol. 35, No. 22, 1996
Notes
Figure 3. Phase transitions in the Ph3E-E′Me3 series and the covalent radius (∆r) differences.
symmetries (S4 and C3) are the principal operators. This rule
is relaxed in the crystals of the bulkier hexaphenyl molecules.
Only hexaphenyldigermane has a metastable hexagonal form
(space group P6322; No. 182).20 Its dominant form crystallizes
in triclinic unit cell (space group P1; No. 1) built up by achiral
bipropellers. If one of the Ge atoms is replaced by Pb, then
the asymmetric Ge-Pb group bearing six phenyl groups exhibits
orientational disorder in a triclinic unit cell isomorphous with
that of Ph3Ge-GePh3.4 The orientational disorder of the Ge-
Pb T Pb-Ge dumbbells generates inversion centers (space
group P1h; No. 2) that result in the shrinkage of the observed
Ge-Pb distances. This distance is still 7.6% longer than the
Ge-Ge bond of 2.437(7) Å, resulting in a homeostructural
packing scheme. When the second Ge atom in Ph3Pb-GePh3
is replaced by a tin atom, a morphotropic phase transition occurs
again. In the monoclinic unit cell (P21/c; No. 14), there are
two symmetry-independent molecules providing the optimum
of close packing.4 The small (∆ ) 0.06 Å) difference between
the atomic radii of Sn and Pb provides ideal conditions for an
orientational disorder developed by Ph3Pb-SnPh3 molecules.
Since the E-E′ distances for Sn and Pb vary only 1% about
2.82(3) Å, these molecules are isometric, as substantiated by
the isostructuralisms of Ph3Sn-SnPh34 and Ph3Pb-PbPh321 with
Ph3Pb-SnPh3.
closely related space groups, I41/a (No. 88) and I4h (No. 82),
but they are no longer isostructural. Only the asymmetric Sn-
Ge dumbbell brings the Ph3Sn-GeMe3 and Ph3Ge-SnMe3 pair
into an isostructural orthorhombic packing.
(B) The bulky hexaphenyl derivatives cannot develop the
optimum packing around their S6 molecular symmetry; they
accommodate themselves in unit cells of lower (triclinic and
monoclinic) symmetries instead. The presence of more than
one molecule in the asymmetric units of Ph3E-E′Ph3 with E )
Sn, Sn, Pb and E′ ) Sn, Pb, Pb, combined with positional
disorder of the asymmetric E-E′ core, seems to serve the same
goal.
(C) An isostructural packing array can be expected among
the Ph3E-E′R3 molecules if they are closely isometric; i.e., E/E′
is either Si/Ge or Sn/Pb (i.e., the unknown Sn-Pb isomers and
the Pb-Pb compound are expected to be isostructural with V).
This is also shown by bulky molecules of the Si/Ge pair even
without any molecular symmetry (e.g., (perchloro-2,2′-biphenyl-
ylene)diphenylsilane and -germane,22 (η5-C5H5)Fe(CO)2SiMe2-
7
SiPh3,23 and (η5-C5H5)Fe(CO)2SiMe2-GePh3 ).
Acknowledgment. Support of this research by the R. A.
Welch Foundation, Houston, TX (Grant AH-546), and the
National Science Foundation (Grant CHE-91-16934) for USA/
East European collaborative research is gratefully acknowledged.
Conclusions
Supporting Information Available: For compound V, tables of
anisotropic thermal parameters, full crystal data and structure refinement
data, atomic coordinates and equivalent isotropic displacement param-
eters, complete bond lengths and angles, and H atoms at calculated
coordinates (5 pages). Ordering information is given on any current
masthead page.
(A) The compact and relatively small Ph4E and Ph3E-E′Me3
molecules reach their bump-in-hollow packing with a relatively
high packing coefficient about 0.73 by inducing their own
molecular symmetry (either S4 or C3) in the crystal lattice. For
long E-C bonds, the close packing of Ph4E homologues
tolerates even the accommodation of the bulky methyl group
in an ortho position (Sn derivative) without altering their
symmetry.3d Even the m- and p-tolyl derivatives crystallize in
IC960791Z
(22) Fajar´ı, L.; Julia´, L.; Riera, J.; Molins, E.; Miravitlles, C. J. Organomet.
Chem. 1990, 381, 321.
(20) Dra¨ger, M.; Ross, L. Z. Anorg. Allg. Chem. 1980, 460, 207.
(21) Preut, H.; Huber, F. Z. Anorg. Allg. Chem. 1976, 419, 92.
(23) Pa´rka´nyi, L.; Pannell, K. H.; Hernandez, C. J. Organomet. Chem. 1983,
252, 127.